1. Field of the Invention
This invention pertains generally to monitoring strain thereon portions of implants positioned within a living being, and more particularly to using strain monitoring as an indicator of medical conditions including, without limitation, monitoring the progress of spinal fusion and measuring spinal loading.
2. Background Art
Lumbar fusion is one of the fastest growing areas of orthopedic surgery. A lumbar fusion is commonly recommended for diagnoses such as, for example, a recurrent disc herniation, lumbar spondylolisthesis, scoliosis or curvature of the spine, severe disc degeneration, or for a traumatic injury of the spine such as a fracture. All of these different conditions can cause back and leg pain, which can result in debilitation and prevents the patient from enjoying ordinary daily activities. Of course, other circumstances or conditions exist in which a fusion is the best treatment for the particular source of back and leg pain.
Lumbar fusion procedures promote the permanent fusion of two or more vertebral bones together to maintain alignment and provide stability and strength. The fusion created linking bridge of solid bone effectively eliminates motion across the damaged level, which results in a reduction of pain experienced by the patient. Lumbar fusion methodologies are conventional and include different approaches to the spine, such as, for example and without limitation, anterior and posterior approaches.
Conventional lumbar fusion methodologies typically use a spinal artificial support that is deployed during surgery. The spinal artificial support is fixed to targeted body tissues and serves as an initial support to help fixate the respective vertebrae of interest until bone growth, which can be stimulated by a bone growth factor, operably fills the area between the respective vertebrae of interest to eliminates motion between the vertebrae. The spinal artificial support can become at least partially encapsulated during the bone growth process.
In one example, a pedicle screw is screwed from the posterior through the pedicle bony bridge of the vertebrae and into the wall the vertebral body. This procedure is repeated for the neighboring vertebrae and bilaterally on the opposite side of the posterior spine. Once all four pedicle screws are in place, a rod or plate is mounted thereon at least two of the pedicle screws. The rod or plate is then held down with locking nuts that screw onto the posts. In another example, an intravertebrael cage can be mounted therein the disk space. In either example, after the spinal artificial support is fixated into the desired position, it is conventional to add bone graft material in and about the intravertebrael space to encourage the growth of bone between the adjacent vertebrae of interest.
The process of healing a fusion can take many months or well over a year to be complete. Conventionally, after surgery, the patient is immobilized with a brace that extends from beneath the arms to midline of the hips and is instructed not to perform any strenuous physical activity for an extended period of time which results is atrophy of the muscles of the spine and abdomen from disuse.
One difficulty is that the biomechanical properties of a stable spinal fusion typically precedes the radiographic appearance of a solid fusion by at least eight weeks, which makes it difficult for a physician to monitor the efficacy of the fusion protocol. However, as the bone-fusion process matures the load-sharing of the spinal artificial support changes. It has been found that the load-sharing of the spinal artificial support, and particularly the bending stress thereon the spinal artificial support decreases concurrently with the development of the spinal fusion.
Presently, the onset of spinal fusion after lumbar surgery continues to be difficult to determine, and, even though the implant provides internal fixation in a much shorter period of time, patients are frequently required to wear the brace for extended periods of time with the resulting detrimental effects to the patient's musculature. There is a need for an approach that allows the physician to monitor the fusion process to maximize the outcome of the spinal fusion process.